At screening, pre-bronchodilator spirometry testing will be followed by post-albuterol/salbutamol spirometry testing. Post-albuterol/salbutamol FEV1 and FEV1/FVC values will be used to determine subject eligibility. To further characterize bronchodilator responsiveness, post-ipratropium testing will be conducted following completion of post-albuterol/salbutamol spirometry.